Seasonal Variation in Equatorial Mesospheric Temperatures Observed by SME

Abstract

Observations made by the Solar Mesosphere Explorer (SME) satellite from 1982 through 1986 are used to examine the seasonal variation of temperature in the equatorial mesosphere between 58.5 and 90 km. Near the equator, seasonal variability is dominated by a strong semiannual oscillation (SAO) whose amplitude increases from about 3 K in the lower mesosphere to 7.3 K near 80 km. Above 80 km, the amplitude of the oscillation decreases to a minimum at 83 km, but increases again sharply above that level, reaching 16,6 K at 90 km, the highest level observed. The structure of the temperature SAO is consistent with previous observations of the SAOs in temperature and zonal wind, although the very large amplitude at 90 km may be due in part to contamination by the diurnal tide. Just below 80 km, temperatures are warm (cold) near the solstices (equinoxes), implying westerly (easterly) accelerations above; the behavior at 58.5 km lap that at 80 km by about 2 months. There is evidence in the data for a seasonal asymmetry in the temperature oscillation, the cycle encompassing Northern Hemisphere winter and spring being strongest. The asymmetry is particularly large in the development of the warm anomaly in the lower mesosphere, which at 60?70 km is over 5 K larger in February than in August. The behavior parallels that documented by Delisi and Dunkerton for the stratospheric SAO, and is consistent with their suggestion that planetary wave driving plays an important role in the development of the oscillation.